Remarkably temperate conditions prevail all the year round, mainly because of the country’s altitude.
RHODESIA, although lying in the heart of South-Central Africa, enjoys a surprisingly comfortable climate – surprising, that is, to visitors from northern climes who associate the tropics with oppressive heat and humidity. In fact, a visitor to Rhodesia is likely to find many unexpected features in its climate and weather.
Remarkably temperate conditions prevail almost all the year round, mainly because of the country’s altitude. Every 300-metre climb brings a decrease in temperature of one to two degrees Celsius, and more than half of Rhodesia lies over 900 m above sea level, with the main centres of population being between 1 200 and 1 500 m.
Because of Rhodesia’s inland position the humidity rarely becomes uncomfortably high, the eastern border being about 160 km from the Indian Ocean, while the Atlantic lies about 1 200 km to the west.
Reduced humidity means fewer clouds and more abundant sunshine. But even sunshine can be excessive, and Rhodesia is fortunate that the mid summer months of December, January and February coincide with the main part of the rainy season, when a certain amount of cloud prevents excessively hot conditions.
Rainfall in tropical countries is basically intense. Yet the overall totals in Rhodesia are not excessive. The country as a whole has a mean annual rainfall of about 685 mm (ranging from half this value in the extreme south to about double at places on the easternborder mountains). The United Kingdom and much of Europe record similar annual totals; and New York, Rio de Janeiro, Tokyo, Melbourne and Durban actually have higher average rainfalls than do most parts of Rhodesia.
Nevertheless, it is in respect of temperatures that the biggest surprises are found. The mean annual temperatures at the four main centres Salisbury, Bulawayo, Gwelo and Umtali – fall within the range of 17 to 19,5°C.
This is about the same as at Sydney, Los Angeles and Cape Town, only slightly warmer than average temperatures at Athens, Johannesburg, Rome, Lisbon, Melbourne, Mexico City and Buenos Aires, and slightly cooler than those at Durban and Brisbane. Rhodesia is of course appreciably warmer, on average, than New York, London and Paris, but much cooler than Rio de Janeiro, Miami, Trinidad, Mauritius and Dar-es-Salaam.
The warmest weather actually occurs during the two – or three – month period immediately before the rainy season. The warmth itself is. nearly always dry, furthermore, this is a pleasantly breezy time of the year.
During the winter months the weather is predominantly fine and sunny and the days are mild. But the nights are surprisingly cool, and even scattered light frost can sometimes occur on mid-winter mornings.
Let’s take a closer look now at the climate, season by season. Both temperature and rainfall are taken into account in defining the Rhodesian seasons, because they do not conform readily to the popular subdivision into summer, autumn, winter and spring.
Winter is the only real exception. In Rhodesia we call it the cool season. It lasts from about the middle of May to the middle of August, a total of three months. Unlike countries in temperate latitudes, there is little difference here in the length of day between summer and winter, and Rhodesia actually has more hours of sunshine per day in the cool season than during the period which conventionally would be known as summer!
The mild sunny days contrast quite sharply, however, with conditions at night. The dryness of the atmosphere is mainly responsible for a wide range between the mid-afternoon maximum temperature and the minimum reached by early morning. The difference frequently amounts to more than 15 degrees Celsius.
Warm coats are therefore commonly worn if one goes out at night. And if one stays at home one is almost certain to make use of the electric radiator, or a log or coal fire (most Rhodesian homes have fireplaces). Pullovers and cardigans are often worn during the first few hours of the morning and slipped on again towards evening.
With the variations in altitude in Rhodesia, from Salisbury at 1 500 m, Bulawayo at 1 400 m, the Victoria Falls at 900 m and Kariba at 760 m, temperatures over the whole country do vary. For this reason, resorts in the low-lying (and therefore warmer) parts of the country are naturally very popular during the cool season.
The fine mild weather is interrupted from time to time by invasions of cold air from temperate latitudes. The north-western half of the country is hardly ever affected, but the southeastern and eastern parts may experience occasional spells of cold overcast weather, with drizzle or rain. On the windward slopes of the Eastern High lands, the rain can be quite heavy on such occasions, but other areas rarely get more than intermittent light drizzle. In extreme cases, daytime temperatures may drop to about 10 degrees C below average for a day or two. Surprisingly though, there is usually a temporary rise in the temperature at night!
Cold air may also reach Rhodesia from the south-west, that is, by an overland route. Even though a south westerly airstream may bring snow to parts of South Africa, it is always very dry by the time it arrives here. With skies remaining clear, the daytime temperatures usually fall only a few degrees. But it becomes much colder at night, and fairly widespread frost is likely to occur under these conditions, the south-west of the country being of course the most vulnerable.
Very occasionally, during the cool season there may be an outbreak of thundery rain, but these conditions are extremely short-lived.
From the middle of August there is generally a definite upward trend in temperature, and the transition from cool season to warm season seldom takes more than three weeks!
The temperature rise during September is liable to be interrupted by a further cold snap but the warm season is usually approaching its peak by mid-October. By then the ladies have stored away all their woollen garments, and are wearing gay cotton frocks. The gentlemen also respond to the rapid change from cool to warm weather – smart “safari suits”, with either long trousers or shorts, are popular and may be seen in all but the most conservative of establishments at this time of the year.
The rapidly rising temperatures have a remarkable effect on the trees as well. The msasas become most attractive with their flush of red or russet foliage (which gradually changes to green during the weeks that follow); in addition, the jacaranda and flamboyant trees burst into bloom in quick succession. These colourful displays take place long before any rain has fallen.
Scattered afternoon showers and thunderstorms may occur, however, during the latter half of the warm season. Although rainfall amounts are mainly small, these isolated storms can be quite violent, being accompanied by strong squalls of wind.
The resorts along the Eastern Highlands (Inyanga, Melsetter, Vumba) are popular during the warm season because of the lower temperatures associated with their altitude.
Towards the end of November or early in December the main rainy season begins. The onset of the main rains is closely linked with the arrival of the so-called “I.T.C.Z.”. This stands for the Inter-Tropical Convergence Zone which migrates north and south as it “follows the sun”, and which favours the development of rain and thunder conditions. It usually extends across the northern half of Rhodesia intermittently for three of four months of the year.
Wet and dry spells tend to alternate, each usually lasting a few days. Occasionally, however, a mild wet spell or a warm dry one may go on rather longer. Although afternoon or evening thunder storms are still the predominant form of precipitation, rain quite often falls during the night and in the early morning. This is particularly the case when “Congo Air” is present. This air-mass reaches Rhodesia by way of the Congo and Zambia, but actually starts off from the South Atlantic Ocean.
Rhodesian weather is periodically affected by tropical cyclones. These intense revolving storms, often hundreds of miles in diameter, which in the North Atlantic are known as hurricanes and in the China Seas as typhoons. A cyclone in the Mozambique Channel exerts a most surprising influence on Rhodesian conditions; more often than not it produces a spell of dry weather! Very occasionally (about once every two are intense revolving storms, often hundreds of miles in diameter, which in the North Atlantic are known as hurricanes and in the China Seas as typhoons. A cyclone in the Mozambique Channel exerts a most surprising influence on Rhodesian conditions; more often than not it produces a spell of dry weather! Very occasionally (about once every two or three seasons) a cyclone moves inland. Heavy downpours and strong winds are then liable to occur at places within about 80 km of the central vortex.
Fortunately, the overland movement tends to weaken the disturbance, and by the time a cyclone enters Rhodesia it has but a fraction of its original intensity Rhodesians are fascinated, rather than awed, by cyclone movements reported in the weather forecasts. The practice of allocating feminine code-names to cyclones has probably fostered this attitude.
Day-to-day temperatures show little variation throughout the main rainy season and, on average, they tend to run several degrees lower than in the preceding warm season.
This does not apply, however, to areas near Rhodesia’s southern borders which experience only fringe effects of the l.T.C.Z.’s presence. Cloudiness and rainfall thus do not exert the same modifying influence as further north, with the result that in the extreme south the mid-summer months are actually the hottest.
With the northward retreat of the I.T.C.Z. around March, Rhodesia’s main rainy season draws to a close. If the rains end prematurely, a minor warm season may follow; but, in general, the post-rainy season is largely transitional between the main rainy season and the cool season; and it usually provides some of the· loveliest weather of the whole year.
Written by: J.B. Hattle – Dept. of Meteorological Services